在对象

Question

我有一个对象：

let names = { field1: 'ton', field2: null }  // or field3 does not exist

我需要将name对象中的变量元素插入到

field='field2'
relative='brotherage'
names[field][relative] =  30;  // has no effect in my code, why ?

得到这个：

 { field1: 'ton', field2: {brotherage: 30 } }

并使用此类代码向字段添加更多元素：

field='field2'
relative='cousinage'
names[field][relative] =  20;  // has no effect in my code, why ?

得到这个：

 { field1: 'ton', field2: {brotherage: 30, cousingage: 30 } }

什么是最好的方法或为什么我失败了...我尝试过很多东西但是我迷路了......

Answer 1

您必须首先使用空对象初始化names[field]：

let names = { field1: 'ton', field2: {} }

field='field2'
relative='brotherage'
names[field][relative] = 30

field='field2'
relative='cousinage'
names[field][relative] = 20

console.log(names)

Answer 2

使用空对象初始化field2字段：

let names = { field1: 'ton', field2: {} }

Answer 3

如果属性具有假值或不存在，则可以使用默认对象。

var names = { field1: 'ton', field2: null },
    field = 'field2',
    field1 = 'field3', 
    relative = 'brotherage';
    relative1 = 'inlaw';
    
names[field] = names[field] || {};
names[field][relative] =  30;

names[field1] = names[field1] || {};
names[field1][relative1] =  40;

console.log(names);

Answer 4

  

//对我的代码没有影响，为什么？

因为names[ "field2" ]是null而你的代码是错误的

  

未捕获的TypeError：无法设置属性＆＃39; brotherage＆＃39;为null

你首先需要让它成为一个对象

names[field] = names[field] || {}; 
names[field][relative] =  30;